The invention relates to a method of forming a recess in a body. In particular, but not exclusively, the invention relates to a method of forming a recess in a metal body to define an opening having an outer periphery of at least partially square or rectangular form.
In a metering valve arrangement of the type used to control fuelling of a compression ignition internal combustion engine, a metering valve member is angularly adjustable within a bore of a metering valve sleeve to vary the degree of overlap between a recess or channel provided in the metering valve member and an outlet port provided in the sleeve so as to vary the rate of flow of fuel to the engine. The metering valve member is of generally solid, cylindrical form except for the provision of the recess. It is known that the sensitivity of the metering valve arrangement is improved if both the outer periphery of the recess in the metering valve member and that of the outlet port in the sleeve with which the recess cooperates are of substantially square or rectangular form.
It has been proposed to use a spark erosion technique using an Electric Discharge Machine (EDM) to form ports or openings of square or rectangular form in the above mentioned components. However, such techniques are time consuming and the manufacturing cost per item is high, and so they are not suitable for large scale manufacture of such items. It has also been proposed to use injection moulding techniques to form such square or rectangular ports but, again, the associated manufacturing costs are prohibitive.
The present invention is aimed at one or more of the problems identified above.
According to the present invention, there is provided a method of forming a recess in a body having a cylindrical surface, the method comprising:
providing a grinding wheel having a first axis, a circumferential surface concave to a second axis that is substantially orthogonal to the first axis and first and second opposing radial surfaces of substantially planar form,
engaging at least a portion of the circumferential surface of the grinding wheel with an outer surface of the body, and
rotating the grinding wheel and the body relative to one another about the first axis to cause a region of the body to be ground by said wheel, thereby to define a recess in the body, having a periphery at the cylindrical surface thereof, which includes at least two substantially square corners and at least one pair of substantially parallel facing edges.
For the purpose of this specification, the phrase xe2x80x98grindingxe2x80x99 shall be taken to refer to any process by which material is ground, milled or otherwise removed from a body through engagement between a rotatable grinding element and the body, and shall therefore be taken to include processes commonly referred to as milling processes in which a toothed milling wheel or disc is brought into engagement with the body and relative rotational movement between the milling wheel and the body causes removal of a portion of the body.
In a preferred embodiment, the first axis forms a drive axis, and the method includes the step of rotating the grinding wheel about the first axis to provide said relative rotation between the grinding wheel and the body. As an alternative, or in addition, the body itself may be rotated or otherwise moved relative to the wheel to provide said relative rotation.
In one embodiment of the invention, the body may be of substantially solid form and may, for example, take the form of a metering valve member for a metering valve arrangement, having a substantially cylindrical outer surface.
If the method is used to provided a recess in a metering valve member having a substantially cylindrical outer surface, an end region of the metering valve member may be ground such that the recess extends to an end surface of the metering valve member and has an outer periphery at the outer surface of the metering valve member having only two square corners.
In an alternative embodiment of the invention, the body may be provided with an internal bore defining a tubular wall having a substantially cylindrical internal surface, and the method may comprise the step of rotating the grinding wheel and the body relative to one another until the recess extends through the tubular wall to define an opening having a periphery at the internal surface of the wall that includes at least two substantially square corners. For example, the body may take the form of a metering valve sleeve for a metering valve member.
The method may be used to provide a recess in a region of the body intermediate opposing end regions of the body such that the recess has a periphery at the internal surface of the tubular wall having four substantially square corners, and two pairs of substantially parallel facing edges, such that the periphery is substantially square or rectangular in shape.
In one preferred embodiment, the circumferential surface of the grinding wheel is shaped such that the outer periphery of the opening defined in the tubular wall has a periphery at the internal surface of the wall having four substantially square corners, and two pairs of substantially parallel facing edges.
It has been found that the provision of cooperable openings of square or rectangular form in the valve member and the sleeve components of a metering valve arrangement improves the sensitivity of the valve.
The body to be ground extends along a further axis, the method preferably comprising the step of rotating the grinding wheel about a first axis which is substantially perpendicular to the further axis.
If required, the method may include the further step of punching or otherwise finishing the periphery to remove any slight anomalies at the corners if they are not quite square.
The present invention provides a convenient method of forming a square or rectangular recess or opening in a metering valve component, and is suitable for large scale component production. In general the method may be utilised for the formation of recesses or openings of square or rectangular form in any component formed from metal, or another material suitable for grinding.